Electrodynamic acoustic transducer
The invention relates to an acoustic transducer generating a sound radiation by compression and expansion of an air mass situated between a mobile membrane and a fixed surface or between two mobile membranes. The present invention concerns a transducer or acoustic loudspeaker of electrodynamic type designed to emit sound waves from a modulated electrical signal. The particular arrangement of the constituent elements of the transducer as presented in the invention enables the generation of an acoustic radiation by compression and expansion of the air mass located between a mobile membrane and a fixed surface or anvil which are distinguished by being placed opposite one another. The direction of the resulting acoustical wave is perpendicular to the direction of displacement of the membrane. This manner of generating an acoustic wave enables the production of transducers with specific electroacoustic directivity characteristics.
The present invention concerns an acoustical transducer or electrodynamic loudspeaker designed to emit sound waves resulting from a modulated signal.
BACKGROUND OF THE INVENTION—FIGS. 1-4. Traditional transducers or loudspeakers (as illustrated in
Another type of transducer the ESS loudspeaker, invented in the U.S.A. by Dr Oscar Heil (the principle being illustrated in
A third type of transducer, (illustrated in
The auditory spectrum perceptible to man from 20 to 20000 hertz approximately is characterized by the very great variety of wavelength differences involved, ranging from one millimeter to several meters. The reproduction of all these frequencies at acceptable level of power must be achieved by means of two or more loudspeakers, each of which is responsible for a part of the sound spectrum. The result of this necessity is that the acoustic centers of these loudspeakers are several decimeters apart. This degrades the precision and spatial restitution of the stereo signal reproduced and introduces a phenomenon of acoustic interference known as directivity lobes, giving rise to very significant variations of acoustic power emitted depending on the position of the listener in relation to the different transducers. This phenomenon accentuates the undesirable directivity characteristics inherent in traditional loudspeakers.
SUMMARY OF THE INVENTION The particular arrangement of the constituent parts of the transducer, subject of the invention, enables the generation of an acoustic radiation according the modulating current applied, by compression and expansion of the mass of air situated between the mobile membrane, flexibly mounted, by means of a suspension arrangement, on a rigid chassis, and a fixed rigid surface herein referred to as anvil, which is also attached rigidly to the same chassis. As this membrane and this anvil are characterized by being positioned opposite one another, the resulting acoustic waves are perpendicular to the direction of the displacement of the membrane. The distance separating the membrane from the rigid fixed surface is slightly more than half the maximum displacement of the membrane, in order to avoid any risk of contact between these two elements. This mode of acoustic sound generation enables the elaboration of electro transducers having characteristics of directivity different to those of traditional loudspeakers. The driving of the membrane according to the modulation current can be achieved by means of an electromagnetic type of drive as shown in the drawings illustrating the invention, but this drive can also be of piezoelectric type (as illustrated in
In order to indicate elements in the different figures that have the same function in different embodiments, the reference numbers appearing on the drawings figures are preceded, in the description and the claims, by the digit of the figure to which this description refers. For example, membrane (9) in
A first embodiment is illustrated in
- A magnetic core (55 and 65) coupled to a magnetic armature (54 and 64) designed to create a magnetic field in between magnetic poles (56 and 66).
- A moving membrane (57 and 67) mounted on a flexible peripheral suspension (58 and 68) incorporating a moving coil (59 and 69) suspended in the air gap (56 and 66). This membrane here illustrated in the form of a convex dome will have a shape commensurate with a high degree of rigidity. This membrane may incorporate fold or corrugations about its periphery, designed to form all or part of its suspension (58 and 68).
- A fixed and rigid surface known as “anvil” (510 and 610), located opposite the mobile membrane (57 and 67) and rigidly attached to (511 and 611) to the chassis or forming an integral part of the latter.
This transducer is characterized by the arrangement of its elements, which create an omnidirectional acoustic transducer, that is to say generating a resulting sound radiation (51 and 61) through 3600 in a plane perpendicular to the direction of displacement (52 and 62) of its membrane. The shape, profile and dimension of the different elements depend on their electrical or mechanical characteristics as well as the spectrum of frequencies to be reproduced. This transducer if it is intended to produce low or medium frequencies may be coupled to an enclosure in order to restitute or absorb the acoustic energy generated at the rear of the membrane.
- A magnetic circuit (75 and 85) coupled to a magnet (74 and 84) resulting in the creation of a magnetic field in an air gap (76 and 86).
- A mobile ring-shaped membrane (77 and 87) mounted on a flexible peripheral internal and external suspension (78 and 88) incorporating a moving coil (79 and 89) suspended in air gap (76 and 86). This membrane may incorporate folds or corrugations about its periphery, designed to form part of its suspension. The
FIGS. 7 and 8 show such an arrangement for its external peripheral suspension. - A fixed and rigid surface, known as anvil (710 and 810) located opposite the mobile ring shaped membrane, (77 and 87) and attached (711 and 811) rigidly to the assembly of other non-moving components of the transducer.
This arrangement with ring-shaped membrane allows the use of the effective surface of the membrane compatible with a high acoustical power whilst avoiding acoustic phase opposition which arises with this type of transducer when the membrane-anvil interface radial length is too close to that of the length of the frequencies to be reproduced. This arrangement is more particularly intended for the reproduction high frequencies that are of short wavelength.
With reference to
The embodiment of the invention represented in
This embodiment comprises
- A rigid chassis (113 and 123).
- A magnet (114 and 124) coupled to magnetic circuit (115 and 125) and designed to create a magnetic field in the air gap (116).
- A mobile membrane (117 and 127) mounted on a flexible suspension including a moving coil (119 and 129) suspending in the air gap, the moving coil being guided by a second suspension (1113 and 1213) designed to ensure centralization of the coil in the air gap.
- A fixed and rigid surface (1110 and 1210) located opposite the mobile membrane and attached rigidly to the chassis or forming an integral part of the latter.
- Baffles (1112 and 1212), rigid or otherwise perpendicular to the membrane and the anvil surface, their role being to physically limit the air mass between the membrane and the anvil. These baffles may form an integral part of the chassis (113 and 123).
This embodiment allows a precise directivity of acoustic radiation according to the form, geometric configuration, and dimensions of the membrane, anvil, baffles and chassis and according to the spectrum of frequencies to be reproduced. This transducer, if designed to reproduce low or medium frequencies, may be coupled to an enclosure (1221) designed to capture or absorb the acoustical energy generated at the rear of the mobile membrane.
The manufacture of this type of transducer is identical to that of traditional acoustic transducers or loudspeakers.
In materials and manufacture:
- Chassis and anvil in metal or synthetic or composite materials or wrought or pressed steel or die cast metals or resin containing fiber for consolidation or strength.
- Membrane in metal, treated or untreated paper, synthetic or composite fibers or non-fibrous materials.
- Suspension in natural or synthetic rubber or other synthetic material. This suspension may equally comprise folds or corrugations formed in the membrane of the transducer.
- Magnets, armatures, magnetic circuits and coils of conventional construction.
- Generally speaking, this description includes all current and future materials and methods of manufacture, adapted to the manufacture and improvement of this type of transducer.
In its applications and uses:
- This will correspond and be adapted to the characteristics and specific functioning of this type of transducer. Drivers of electromagnetic, peizoelectric, electrostatic or other type, as well as analog or digital processes of control and driving of all mobile parts, may be applied to this type of transducer.
- The type of transducer as presented in the invention may include a device commonly called a “horn” which enables the enhancement of its power output by an improved acoustic coupling between the membrane and the ambient air by a progressive transition of pressures.
- The type of transducer as presented in the invention may be utilized in other fluid media, gas or liquid other than air.
Claims
1-8. (canceled)
9. An electroacoustical transducer comprising:
- a chassis (3);
- a rigid surface (10) rigidly attached to said chassis (3);
- a moving membrane (7), attached flexibly to said chassis (3) and positioned to face said rigid surface (10), with an air mass between said rigid surface (10) and said moving membrane (7); and
- a driving device (4,5,9,9b) to displace said moving membrane (7) in the direction of said rigid surface activated by a modulating electric current;
- the displacement of said membrane (7) generating, by compression and expansion of said air mass, an acoustic wave, of which the direction of propagation (1) is essentially perpendicular to the direction (2) of displacement of said membrane (7).
10. An electroacoustical transducer as set forth in claim 9, wherein
- said rigid surface (10) and said moving membrane (7) are configured in cylindrical symmetry about an axis that is parallel to the direction (2) of displacement of said moving membrane (7); and
- the distance between said rigid surface (10) and said moving membrane (7) increases from the center of the periphery;
- the resulting sound radiation being omnidirectional in a plane perpendicular to said direction (2) of displacement of said moving membrane (7).
11. An electroacoustical transducer as set forth in claim 9, wherein said rigid surface (10) is shaped in the form of a convex dome.
12. An electroacoustical transducer according to claim 11, wherein said moving membrane (7) also is shaped in the form of a convex dome.
13. An electroacoustical transducer as set forth in claim 11, wherein said moving membrane (7) is ring shaped.
14. An electroacoustical transducer according to claim 9 comprising acoustic screens or baffles (12) arranged to be in a plane that is perpendicular to said moving membrane (7) and said rigid surface (10), in such a way as to limit the air mass contained between them, the resulting sound radiation being directional.
15. An electroacoustical transducer as set forth in claim 9, comprising an acoustic horn that enables the improvement of the acoustic coupling between moving membrane (7) and the ambient air.
16. An electroacoustical transducer as set forth in claim 9, wherein said device of driving is an electromagnetic (4,5,9), piezoelectric, (9b) or electrostatic device.
17. An array consisting of multiple electroacoustical transducers as set forth in claim 9, each adapted to the reproduction of a determined range of frequencies, stacked on an axis that is parallel to the direction of displacement of said moving membrane (7).
Type: Application
Filed: Feb 6, 2004
Publication Date: Jul 6, 2006
Patent Grant number: 7426281
Inventor: Patrick Hoffmann (Villons-les-Buissons)
Application Number: 10/544,177
International Classification: H04R 1/20 (20060101);